JP2006278184A - Square battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a square battery suppressing the bulging of a battery can by suppressing the returning force of a winding electrode body after compression molding together with the reduction of a manufacturing cost by shortening working time in winding or compression molding, and to provide the manufacturing method of the square battery. <P>SOLUTION: In the square battery formed by housing an oblong wound electrode body 3 formed by winding and pressing a positive electrode 31 and a negative electrode 33 through a separator 32 in an outer can 1, a ratio (L4/L5) of the electrode thickness L4 in the wide width direction to the electrode thickness L5 in the narrow width direction in the wound electrode body 3 is regulated to less than 1.2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a prismatic battery in which an elliptical winding electrode body in which a positive electrode and a negative electrode are wound and pressurized via a separator is housed in an outer can, and a method for manufacturing the same.

2. Description of the Related Art In recent years, electronic devices such as mobile phones, notebook computers, and PDAs have been reduced in size and weight, and along with this, reduction in size and weight of batteries used in electronic devices has been demanded. In this case, the prismatic battery is more widely used because it has better storage efficiency than the cylindrical battery.
Here, as a method for producing the wound electrode body housed in the rectangular outer can of the rectangular battery, the following methods are known.

(1) As shown in Patent Document 1 below, a long sheet-shaped positive electrode, a long sheet-shaped negative electrode, and a separator that insulates both electrodes are wound using a flat core, and then A method of producing an oval winding electrode body by extracting the winding core.
(2) The same positive and negative electrodes as in (1) above and a separator are wound using a winding core having a circular cross section, and after removing the winding core, the electrode body is crushed from the diameter direction to increase the cross sectional shape. A method of making a wound electrode body in a circular shape. Further, as shown in Patent Document 2 below, a method of high-temperature compression molding when crushing the winding electrode body from the diameter direction is also known.

JP-A-6-96801

Japanese Patent Laid-Open No. 10-302827

However, the above prior art has the following problems.
(1) Technical Problem Since the tension control is difficult in the technique (1), the winding speed is slower than in the case of winding into a cylindrical shape. There was a problem that the manufacturing cost of the type battery increased.

(2) Technical Problems In the technique (2), since the circular winding electrode body is directly formed into an oval shape, it takes a long time to perform compression molding to a predetermined thickness, and after compression molding There was a problem that the battery can that accommodates the take-up electrode body swells due to the force of the take-up electrode body to return to a circular shape. Such a problem is particularly noticeable in a large battery having a large number of turns and requiring large current charge / discharge.

  The present invention has been made in order to solve the above-mentioned problems, and shortens the working time at the time of winding or compression molding, thereby reducing the manufacturing cost and winding the electrode body after compression molding. It is an object of the present invention to provide a prismatic battery and a method for manufacturing the same that can prevent the battery can from swelling by suppressing the restoring force of the battery.

In order to achieve the above object, the invention according to claim 1 of the present invention is characterized in that an oval winding electrode body in which a positive electrode and a negative electrode are wound and pressurized via a separator is disposed in an outer can. In the accommodated prismatic battery, the ratio of the electrode thickness in the wide direction to the electrode thickness in the narrow direction in the winding electrode body is restricted to less than 1.2.
With the above configuration, since the shape of the oval winding electrode body in the hollow portion becomes wider, the force to return to the cylindrical shape is reduced, and the battery can bulge is alleviated. .

The invention described in claim 2 is the invention described in claim 1, characterized in that the number of windings in the winding electrode body is 40 or more.
As in the above configuration, in a large-capacity battery, the coating thickness is reduced in order to achieve high output, but there is a high possibility that the influence of bulging will appear due to the large number of windings (usually 40 times or more). If it is the structure of Claim 1, the force which tries to return to a cylindrical shape will become small, and a battery can swelling will be relieved.

  In order to achieve the above object, the invention according to claim 3 of the present invention is characterized in that the positive electrode and the negative electrode are wound through a separator in a state where a hollow portion is left in the center, and a spiral winding is performed. A first step of producing an electrode body; a second step of expanding the cavity in a direction away from the axis of the winding electrode body; and compressing the winding electrode body from the outside to lengthen the winding electrode body A method for manufacturing a rectangular battery, comprising: a third step of forming a circular shape; and a fourth step of storing the winding electrode body in an outer can.

  As in the above method, after the first step of producing the spiral wound electrode body with the cavity remaining in the center, there is a second step of expanding the cavity in the direction away from the axis of the wound electrode body. Therefore, at the time of compression molding in the third step, the innermost peripheral portion of the winding electrode body has an oval shape. Therefore, after the take-up electrode body is stored in the outer can in the fourth step, the force for the take-up electrode body to return to the cylindrical shape is reduced, so that the battery can bulge is alleviated.

The invention described in claim 4 is the invention described in claim 3, characterized in that the number of windings in the first step is 40 or more.
If it is the said method, there exists an effect similar to the effect of Claim 2.

According to a fifth aspect of the present invention, in the third or fourth aspect of the present invention, in the second step, the two spreading members are brought into contact with the winding electrode body in the cavity and separated from the axis of the winding electrode body. The cavity is widened in the direction.
Since the innermost peripheral portion of the take-up electrode body is formed into an oval shape simply by spreading the take-up electrode body with the two spreading members, the step of the second step can be easily performed.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, a portion of the spreading member that contacts the winding electrode body is formed in an arc or an ellipse.
As described above, if the portion of the spreading member that contacts the winding electrode body is an arc or an ellipse, it is possible to suppress the winding electrode body from being damaged in the second step.

  According to the present invention, the battery can can be obtained by suppressing the return force of the wound electrode body after compression molding while reducing the manufacturing cost by shortening the working time during winding and compression molding. There is an excellent effect that swelling can be suppressed.

  Hereinafter, the content of the present invention will be described in more detail with reference to FIGS. 1 to 4, but the present invention is not limited to the following best modes, and may be appropriately changed within the scope not changing the gist thereof. Can be implemented.

1 is a perspective view of a lithium ion secondary battery according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, FIG. 3 is an exploded perspective view of a winding electrode body, and FIG. ) To (d) are explanatory diagrams of the manufacturing process of the wound electrode body.
As shown in FIG. 1, an oval shape is formed in a storage space constituted by an outer can 1 having a bottomed rectangular tube shape and a sealing plate 2 fixed to the opening of the outer can 1 by a laser welding method. The winding electrode body 3 is arranged.

As shown in FIG. 3, the take-up electrode body 3 is formed by interposing a strip-shaped separator 32 between a strip-shaped positive electrode 31 and a negative electrode 33, winding them in a spiral shape, and further expanding the process. Etc., and is configured to have an oval shape. The positive electrode 31 is configured by applying a positive electrode active material 34 made of lithium composite oxide (LiCoO ₂ ) to both surfaces of a band-shaped core 35 made of aluminum foil, and the negative electrode 33 is made of a band-shaped core 37 made of copper foil. The negative electrode active material 36 containing a carbon material is applied to both sides of the substrate. The separator 32 is impregnated with a non-aqueous electrolyte.

  Here, the positive electrode 31 is formed with a coated portion where the positive electrode active material 34 is applied and a non-coated portion where the positive electrode active material is not applied. The negative electrode 33 also has a coated portion where the negative electrode active material 36 is applied and a non-coated portion where the negative electrode active material is not applied. The positive electrode 31 and the negative electrode 33 are superimposed on the separator 32 while being shifted in the width direction, and the uncoated portions of the positive electrode 31 and the negative electrode 33 are projected outward from both end edges of the separator 32, respectively. The take-up electrode body 3 is formed by taking up in a shape.

  As a result, in the winding electrode body 3, the core body 38 of the non-coated portion of the positive electrode 31 is outside the one end edge of the separator 32 at one end of the both ends in the winding axis direction. (Hereinafter, the protruding core part of the positive electrode may be referred to as a positive electrode side protruding core 39a), and the core 39 of the non-coated part of the negative electrode 33 is a separator at the other end. 32 has a structure projecting outward from the other end edge of 32 (hereinafter, such a projecting core portion of the negative electrode may be referred to as a negative-side projecting core body 39b).

  As shown in FIG. 2, a positive electrode current collector 4 is attached to the positive electrode side protruding core 39a. The positive electrode current collector 4 includes a positive electrode terminal 10 fixed to the sealing plate 2 and a positive electrode lead plate. 18, while the negative electrode side protruding core body 39 b is attached with a negative electrode current collecting member 5, and the negative electrode current collecting member 5 is fixed to the sealing plate 2. 11 and the negative electrode lead plate 19 are electrically connected. The positive terminal 10 is fixed to the sealing plate 2 by the nut 7 through the insulating packing 6, and the negative terminal 11 is fixed to the sealing plate 2 by the nut 9 through the insulating packing 8.

  The sealing plate 2 has a plate shape, and a safety valve 15 and a liquid injection port 16 are provided in a substantially central portion. The safety valve 15 has a dome shape that is thinner than other parts, and when the internal pressure of the battery exceeds a predetermined value, the safety valve 15 is crushed to release the gas in the battery to the outside of the battery. It is. The liquid injection hole 16 is fitted with a liquid injection stopper 17 for sealing the inside of the battery.

Here, the lithium ion secondary battery having the above structure was produced as follows.
Preparation of positive electrode First, a lithium composite oxide (LiCoO ₂ ) powder having an average particle diameter of 5 μm as a positive electrode active material and artificial graphite as a conductive agent are mixed at a mass ratio of 9: 1 to obtain a positive electrode mixture. Obtained. Next, after the polyvinylidene fluoride as an adhesive was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare an NMP solution, the mass ratio of the positive electrode mixture to the polyvinylidene fluoride was 95: 5. The positive electrode mixture and the NMP solution were mixed so that a slurry was prepared. Thereafter, this slurry is applied to both surfaces of an aluminum foil having a thickness of 20 μm to be a positive electrode core by a doctor blade method (however, a fixed width non-coating portion where slurry is not applied to the end in the width direction of the aluminum foil) In addition, the cathode 31 was produced by vacuum drying at 150 ° C. for 2 hours.

-Production of negative electrode First, carbon powder (d ₀₀₂ value = 3.356Å; Lc value> 1000) was jetted and pulverized to produce carbon powder. Next, polyvinylidene fluoride as a binder was dissolved in NMP to prepare an NMP solution, and a slurry was prepared by kneading so that the mass ratio of the carbon powder to the polyvinylidene fluoride was 85:15. . Next, this slurry was applied to both surfaces of a 20 μm thick copper foil serving as a negative electrode core by a doctor blade method (however, a non-coated portion having a constant width where no slurry was applied to the end in the width direction of the copper foil) Further, the negative electrode 33 was produced by vacuum drying at 150 ° C. for 2 hours.

Electrolytic solution volume ratio and preparation of ethylene carbonate and diethyl carbonate 1: mixed solvent at a ratio of 1, by dissolving LiPF ₆ at a rate of I mol / L, to prepare an electrolytic solution.

Battery Assembly First, as shown in FIG. 4A, a separator 32 made of an ion-permeable polypropylene microporous film is wound several times around a winding core 21 having a diameter L1 = 20 mm. The separator 32, the positive electrode 31, the separator 32, and the negative electrode 33 are overlapped so as to be interposed between the negative electrode 31 and the negative electrode 33, and these are wound in a spiral shape 60 times, and then the core 21 is removed. The wound electrode body 3 was produced (the diameter L2 of the wound electrode body = 40 mm). At this time, the positive electrode 31 and the negative electrode 33 are respectively superimposed on the separator 32 while being shifted in the width direction, and the uncoated portions of the positive electrode 31 and the negative electrode 33 are protruded outward from both end edges of the separator 32, respectively. Rolled up. Next, as shown in FIG. 2B, two cylindrical shafts 22 (diameter L3 = 5 mm) as expansion members are inserted into the core hole 23, and the two shafts are expanded to the left and right. Thus, as shown in FIG. 3C, the cylindrical winding electrode body 3 was formed into an oval shape. Thereafter, as shown in FIG. 4D, compression molding was performed to obtain predetermined dimensions.

  Thereafter, the positive electrode current collecting member 4 was attached to the positive electrode side protruding core body 39a of the winding electrode body 3, and the negative electrode current collecting member 5 was attached to the negative electrode side protruding core body 39b. In parallel with this, the positive terminal 10 is fixed to the sealing plate 2 by the nut 7 through the insulating packing 6, and the negative terminal 11 is fixed to the sealing plate 2 by the nut 9 through the insulating packing 8, and then both terminals A positive electrode lead plate 18 and a negative electrode lead plate 19 were attached to 10 and 11, respectively.

  Thereafter, the positive electrode current collecting member 4 and the negative electrode current collecting member 5 were welded to the positive electrode lead plate 18 and the negative electrode lead plate 19, respectively. Next, the wound electrode body 3 in this state was accommodated in the outer can 1, and the sealing plate 2 was covered with the opening of the outer can 1, and the sealing plate 2 was welded to the outer can 1. Finally, after injecting the electrolytic solution from the liquid injection hole 16 of the sealing plate 2, the liquid injection hole 16 was sealed with a liquid injection stopper 17, thereby producing a lithium ion secondary battery in the state shown in FIG.

(Example)
As an example, the lithium ion secondary battery shown in the best mode for carrying out the invention was used.
The battery thus produced is hereinafter referred to as the present invention battery A.

(Comparative example)
As shown in FIGS. 5A and 5B, compression molding is performed after the winding electrode body 3 is manufactured (the step of expanding the winding electrode body 3 to the left and right using the shaft before compression molding is not provided). Except for this, a lithium ion secondary battery was produced in the same manner as the battery of the present invention.
The battery thus produced is hereinafter referred to as comparative battery X.

(Experiment 1)
In the present invention battery A and comparative battery X, the thickness of the battery can immediately after the battery production and the thickness of the battery can after 1 day in each battery were measured, and the swelling amount of the battery can after 1 day was calculated. The results are shown in Table 1.

  As is clear from Table 1, the battery A of the present invention had a battery expansion amount of 0.1 mm and hardly expanded, whereas the comparative battery X had a battery expansion amount of 0.6 mm and greatly expanded. It is recognized that This is because in the wound electrode body of the present invention battery A, the wound electrode body is expanded to the left and right from the winding core hole portion before compression molding, and is formed into an oval shape. On the other hand, in the wound electrode body of the comparative battery X, since the cylindrical wound electrode body is directly compression-molded, it is considered that the thickness recovery after compression molding is not relaxed. . In addition, the battery A of the present invention has an advantage that the time for compression molding to a predetermined thickness can be shortened as compared with the comparative battery X.

(Experiment 2)
In the present invention battery A and comparative battery X, the ratio of the electrode body thickness in the wide direction (L4 in FIG. 6) to the electrode body thickness in the narrow direction (L5 in FIG. 6) (L4) in the wound electrode body after compression molding / L5, which may be hereinafter referred to as the electrode body thickness ratio), and the results are shown in Table 2.

As apparent from Table 2, in the battery A of the present invention, the electrode body thickness ratio is as small as 1.05, whereas in the comparative battery X, the electrode body thickness ratio is as large as 1.2 to 1.25. It is recognized that This is because, in the comparative battery X, the winding electrode body is not expanded in the left and right directions from the winding core hole portion before the compression molding, so that the electrode in the inner peripheral portion in the wide direction is loosened during the compression molding. On the other hand, in the battery A of the present invention, since the winding electrode body is expanded from the core hole portion to the left and right before the compression molding, the electrode in the inner peripheral portion in the wide direction is loosened during the compression molding. This is probably because it is difficult to occur.
Further, when the electrode body thickness ratio is as described above, the battery A of the present invention is wider in the hollow portion of the oval winding electrode body than the comparative battery X (L6 in FIG. 6). Therefore, the force to return to the cylindrical shape is reduced. Therefore, the swelling of the battery is suppressed.

(Experiment 3)
In the present invention battery A and comparative battery X, the total thickness of the electrode body in the narrow direction immediately after compression molding (L7 in FIG. 7) and the total thickness of the electrode body in the narrow direction after the passage of one day were measured, and the following formula Since the thickness recovery rate shown in (1) was examined, the results are shown in Table 3.
Thickness recovery rate = (1− [total thickness of electrode body in narrow direction immediately after compression molding / total thickness of electrode body in narrow direction after 1 day]) × 100 (%) (1)

As is apparent from Table 3, it can be seen that the battery A of the present invention has a small thickness recovery rate of 8%, whereas the comparative battery X has a large thickness recovery rate of 15%. This is the same reason as in Experiment 2. In other words, in Comparative Battery X, the winding electrode body was not expanded in the left and right directions from the core hole before compression molding, so that it was not compressed. The stress in the wide direction is not relieved after molding, but in the battery A of the present invention, the winding electrode body is expanded left and right from the winding core hole part before compression molding, so that the width is increased after compression molding. This is thought to be due to the fact that the direction stress is relieved.
As described above, the battery A of the present invention has a smaller thickness recovery rate than that of the comparative battery X, so that swelling of the battery is suppressed.

[Other matters]
(1) In the above-described embodiment, a cylindrical member is used as the spreading member (shaft 22). However, the member is not limited to this and may be a plate member. However, when a plate-shaped member is used, it is desirable that the portion in contact with the winding electrode body is an arc or an ellipse in order to prevent the winding electrode body from being damaged. Moreover, when the spreading member is cylindrical, the diameter is not limited to 5 mm, and may be about 3 to 6 mm.

(2) The battery to which the present invention can be applied is not limited to the lithium ion secondary battery, but other types of secondary batteries such as nickel-cadmium storage batteries and nickel-hydrogen storage batteries, dry batteries, lithium batteries, and the like. The present invention can be widely applied to primary batteries.

  The present invention can be applied not only to a driving power source of a mobile information terminal such as a mobile phone, a notebook computer, and a PDA, but also to a large battery such as an in-vehicle power source of an electric vehicle or a hybrid vehicle.

It is a perspective view of the lithium ion secondary battery in one Example of this invention. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. It is a disassembled perspective view of a winding electrode body. It is manufacturing process explanatory drawing of a winding electrode body. It is manufacturing process explanatory drawing of the winding electrode body of a comparative battery. It is explanatory drawing which shows the electrode body thickness of a narrow direction, and the electrode body thickness of a wide direction. It is explanatory drawing which shows the electrode body total thickness of a narrow direction.

Explanation of symbols

1: Exterior can 3: Winding electrode body 31: Positive electrode 32: Separator 33: Negative electrode

Claims (6)

In the rectangular battery in which the positive electrode and the negative electrode are wound and pressed through a separator, and an elliptical winding electrode body is housed in an outer can,
The ratio of the electrode thickness of the wide direction with respect to the electrode thickness of the narrow direction in the said winding electrode body is controlled by less than 1.2, The square battery characterized by the above-mentioned.   The prismatic battery according to claim 1, wherein the winding electrode body has 40 or more windings. A first step of producing a spiral wound electrode body by winding a positive electrode and a negative electrode through a separator while leaving a hollow portion in the center;
A second step of expanding the cavity in a direction away from the axis of the winding electrode body;
A third step of compressing the winding electrode body from the outside and molding the winding electrode body into an oval shape;
A fourth step of storing the wound electrode body in an outer can;
A method for producing a prismatic battery, comprising:   The manufacturing method of the square battery of Claim 3 whose winding frequency | count in the said 1st step is 40 times or more.   5. The square shape according to claim 3, wherein, in the second step, the two spreading members are brought into contact with the winding electrode body in the hollow portion, and the hollow portion is widened in a direction away from the axis of the winding electrode body. Battery manufacturing method. The method for manufacturing a prismatic battery according to claim 5, wherein a portion of the push-out member that contacts the winding electrode body forms an arc or an ellipse.